Characteristics of electroluminescent (EL) devices were improved dramatically using indium tin oxide (ITO) chemically modified with H-, Cl-, and CF3-terminated benzoyl chlorides. By the use of reactive –COCl groups, ITO surfaces were modified quickly and the work function of the modified ITO was changed widely depending upon the permanent dipole moments introduced in the para- position of benzoyl chloride. We also compared the performance of the EL devices with ITO modified with different binding groups (–SO2Cl, –COCl, and –PO2Cl2) of p-chlorobenzene derivatives. Finally, we examined the correlation between the change in the work function and the performance of the EL devices by the chemical modification and found that the enormous increase in ITO work function up to 0.9 eV is possible using phenylphosphoryl dichloride with a CF3-terminal group in the para-position.

We demonstrate here that luminance increased more than linearly with an increase in current density of tris(8-hydroxyquinoline) aluminum (Alq3)-based electroluminescent (EL) devices and the EL efficiency reached ∼5 cd A−1 at 250 mA cm−2 when electron and hole injection was well balanced. The luminance–current curves were well fitted with a combination of a linear and a quadratic function of the current. The quadratic component can be attributed to additional singlet excited state (1Alq3*) formation through triplet–triplet (T–T) annihilation of triplet excited states (3Alq3*). The requirement of the well-balanced charge injection implies that the long-lived A4lq3* was quenched efficiently by energy transfer to excess and colored Alq3−⋅ anion or Alq3+⋅ cation radicals in the emission zone when the charge injection was unbalanced. The short-lived A3lq3* was not quenched appreciably.

An SbCl5-doped N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD) thin film was studied as a hole-injection layer in low-molecular-weight organic electroluminescent (EL) devices. EL characteristics of devices with a TPD hole-injection layer doped with other oxidizing reagents, such as iodine, FeCl3, and tris(4-bromophenyl)aminium hexachloroantimonate were compared with that of SbCl5-doped TPD. The device with SbCl5-doped TPD on a cleaned indium–tin–oxide (ITO) substrate exhibited the best performance of all the devices studied. The improvement in device performance was attributed to an increase in work function of ITO due to acid formation as a result of hydrolysis of SbCl5 and by thinning the tunneling barrier for hole injection due to formation of the space charge region in highly doped TPD with SbCl5.

No abstract

The effects of new insulating materials of lithium fluoride and lithium carboxylates at an aluminum cathodic interface on the performance of organic electroluminescent (EL) devices are described. Three different cathode interface materials are used: lithium salts of fluoride, acetate, and benzoate. We compare the current density–voltage (I–V) and the luminance–voltage (L–V) characteristics of the devices with Al/lithium carboxylates with those of the devices with Al/LiF or an Al cathode. We find that the bilayer cathodes with lithium carboxylates exhibit better device performance than the cathodes with LiF or the Al cathode itselt. In particular, the device with lithium benzoate gives the best performance of all the devices studied. The improvements are attributed to the lowering in work function of the cathode due to lithium metal formation by the higher reactivity of lithium carboxylates than LiF, with hot Al atoms impinging on these insulating materials.

To understand the origin of the open-circuit voltage of heterojunction photovoltaic (HJ-PV) cells with small-molecular-weight organic thin films, HJ-PV cells with ITO/donor (20 nm)/fullerene (40 nm)/bathocuproine (10 nm)/Al were studied using three kinds of donors and four types ITOs with different work functions.Since the first report of an organic photovoltaic (PV) cell with the donor (D)/acceptor (A) heterojunction (HJ) by Tang, 1 organic PV cells have attracted attention owing to their ease of fabrication, potential for low-cost productions, and compatibility with flexible substrates.2 A fundamental understanding of the excitonic nature of organic materials is essential for device engineering.2d By the introduction of device concepts such as the mixed 3a and blended 3b,3c DA HJs, the exciton-blocking layer (EBL), 3d and the tandem cell, 3e the performance of small-molecular-weight 2b and polymer 2c,2e organic PV cells has been improved dramatically.To achieve high power conversion efficiencies of such PV cells, the increase in the open-circuit voltage (V oc ) as well as the short-circuit current density (J sc ) and the filling factor (FF) is required. However, the origin of V oc is not well understood. 2,4aFor metal/insulator/metal (MIM) type PV cells, the built-in potential (V bi ) results from the work function difference Á between the electron-collecting (EC) and hole-collecting (HC) electrodes. For so-called ''bulk HJ'' (Type I) PV cells, Al or Ag with low work functions () (4.2 or 4.3 eV) in contact with an A molecule [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) blended with one of various conjugated D polymers is used as the EC electrode, while the polymer film of poly(3,4-ethylenedioxythiophene (PEDOT) doped with poly-(styrenesulfonate) (PSS) acts as the HC electrode. of PEDOT:PSS (5.2-5.3 eV) is higher than that of indium-tinoxide (ITO) (4.5-4.8 eV). Therefore, Á is kept almost constant to be %1:0 eV, since the Fermi level of the metal electrode is considered to be pinned to the lowest unoccupied molecular orbital (LUMO) level of PCBM (4.2-4.3 eV).2c,4a Under such high Á in Type I cells, V oc has been found to change linearly with the highest occupied molecular orbital (HOMO) level or the oxidation potential (E ox ) of Ds. 2c,4b In contrast, Á is 0.3-0.6 eV for HJ small-molecular-weight organic thin film PV (Type II) cells (i.e., ITO/D/A(C 60 )/bathocuproine(BCP)/Al(or Ag)), 2a where the bare ITO electrode is mainly used as the HC electrode and the BCP layer functions as EBL and improves electron transport from the C 60 film to the EC electrode. 3d,5 Recently, V oc of Type II cells with a boron subphthalocyanine chloride (SubPc) D layer was found to be so low as 0.57-0.58 eV, 6 although HOMO of SubPc was estimated electrochemically to be 5.6 eV and thus V oc was expected to be >1:0 V from the V oc vs. HOMO level (or E ox ) relationship described above. It was also found that closer values (0.97-0.98 V) to the expected V oc were measured only when the thickness of the D layer became very t...

The authors report the use of chemically modified indium tin oxide (ITO) with different binding groups (–COCl and –PO2Cl2) of p-chlorobenzene derivatives forming effective monolayers to control the work function of ITO and hence to enhance the hole injection. The enhanced hole injection is studied by measuring current density–voltage (J-V) characteristics. The behavior of J-V characteristics caused by varying the ITO work function in hole-only single-carrier devices with a hole transport layer of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine is examined. Upon grafting with p-chlorophenylphosphoryl dichloride, the J-V characteristics show a space-charge-limited conduction behavior. Such modified ITO anodes lead to improvements in the device properties.

In vitro studies showed that TPP-DTX and its NP primarily accumulated in the mitochondria; generated high reactive oxygen species, leading to mitochondrial disruption and cell apoptosis; and had a higher cytotoxicity against cancer cells. In vivo antitumor studies indicated that the NP significantly suppressed tumor growth compared with free drugs in xenograft tumor-bearing mice. Our results demonstrated that TPP-DTX@FA-chol-BSA NPs could be a promising mitochondria-targeted anticancer prodrug for chemotherapy.